Oxide reduction and diffusion in Fe-Cr alloy honeycombs

Abstract
The goal of this study is to develop practices for evaluating and predicting the microstructural evolution of directly reduced iron-chromium alloys. This fundamental knowledge is being applied to a process developed at the Georgia Institute of Technology to fabricate metal honeycomb extrusions. A paste composed of oxide powders, binders and lubricants is extruded through a die of the desired cross-section and subsequently reduced to metal with hydrogen. The effects of time, temperature and composition on the extent of reduction and diffusion in reducing Fe₂O₃-Cr₂O₃ powder mixtures is investigated. The thermodynamics and kinetics of Fe₂O₃-Cr₂O₃ reduction are evaluated in terms of the free energy of formation as well as reducing species. The kinetics of the microstructural changes are evaluated through diffusion measurements. A thermodynamic model for Fe₂O₃-Cr₂O₃ was developed and used to determine the maximum amount of Cr₂O₃ that would reduce when in contact with iron as a function of the ratio . Diffusion studies consisted of Fe-Cr₂O₃ couples held at temperature in a reducing atmosphere. Cr diffusion in Fe showed a concentration dependence for the geometries investigated.